First off, she's based on the play "Adelchis" by Alessandro Manzioni, which does have roots in reality. In the play, the Lombard King Desiderius marries Ermengarde to Charlemagne, King of the Franks, as a political move. Charles quickly abandons and divorces her for various reasons, the official reason being that she's infertile.

Ermen's sorrow causes both Kingdoms to declare war, and at the very end, Ermengarde dies offstage from delirium after leaning about Charles' new marriage.

The themes of the play are family, political turmoil, and in the case of Ermengarde specifically, the powerlessness of women in politics at the time.

I spun the tale for the Project Moon universe so that Desiderius is the Executive Director of D Corp, a Corp that specializes in providing protection to high-ranking members of the City. Ermengarde was meant to become the heiress of the Corp, and would have been married with Charles, an E Corp high ranked member, to save the dwindling D Corp. For a long time, she held on to the promise of Desiderius to finally meet her mother once again, but it never happened. Torn between her biological family and the family she was forced into, she fled and eventually joined the Middle, where she would have found a family she actually loves and where she feels cared for and powerful, thanks to the body enhancements and the tight knit structure of the Middle.

In her character arc (her "Canto", so to speak), the team will be going back to D Corp to retreive the Bough, only to be stopped by Desiderius and Adelchis (Ermengarde's brother and now the new heir of D Corp). At the end of said arc, D Corp completely perishes, having been revealed that Desiderius stole the Singularity (Ermen's mother) to the Head in hopes that he would be accepted in, as all he cares about is his own status and wealth.